HIV-1 infection is associated with dramatic alteration in gut microbiome composition. Gut microbiome dysbiosis has been associated with pathologies prevalent in HIV-infected individuals including metabolic disease and chronic inflammation. We and others have shown that the gut microbiome of HIV-infected individuals in the US has decreased proportions of the Bacteroides genus and increased Prevotella. In a currently funded R01, we are exploring whether this Prevotella rich/Bacteroides poor (PrevR/BacP) microbiome is related to metabolic disease in HIV patients, specifically lipodystrophy. One factor that complicates the notion that a PrevR/BacP microbiome is related to disease, is that it is also common in health. We have shown that fecal microbiome composition of HIV-positive individuals in the US is strikingly similar to that of healthy individuals in Agrarian populations in Malawi and Venezuela. In the US, individuals with a related PrevR/BacP gut microbiome comprise ~18% of healthy adults and consume diets rich in carbohydrates and low in animal products. Our overarching hypothesis is that HIV-1 infection disrupts adaptive immune responses in the gut that are crucial for promoting colonization of protective bacteria in the context of a Western High Fat Diet (HFD), resulting in a diet/microbiome mismatch which in turn leads to local and systemic inflammatory responses and metabolic disease. We will investigate this hypothesis by conducting three Specific Aims. First, we will examine the relationship between fecal microbiome composition, diet, and inflammatory/metabolic disease markers in HIV-infected subjects pre and post antiretroviral therapy (ART) and HIV-negative controls in rural and urban Zimbabwe using high-throughput 16S ribosomal RNA (rRNA) targeted gene sequencing. This will be the first study to evaluate rural and urban populations in sub-Saharan Africa where the majority of the world's HIV-infected individuals reside and will begin to produce an understanding of how a Westernization of diet in urban centers in the developing world may influence HIV pathogenesis and metabolic co-morbidity. Second, we will assess the effect of short-term diet modification with Agrarian versus Western-like diets on microbiome composition and inflammatory/ metabolic disease markers in ART-treated HIV-infected subjects and HIV-negative controls in the US. This will help to determine whether dietary modulation may be an effective strategy for treating metabolic/inflammatory co-morbidities in HIV-patients. Third, we will examine the role of IL-10 producing CD4+ T regulatory cells (Tregs/Tr1) in microbiome compositional changes that occur with HIV-infection and systemic inflammation. This will help to elucidate driving factors for and consequences of the microbiome changes that occur with HIV infection. The findings from this study could have far reaching implications that extend well beyond HIV infection, by shedding light on how diet and the immune system interact to shape gut microbiome composition in health and disease.